How to add new attribute to ActiveRecord

Question

After getting all values from model, I want to add another custom attribute to the ActiveRecord class (this attribute is not a column in db) so that I could use it in view, but rails does not allow me to add one. What should I add in its model class?

@test.all

@test.each do |elm|
    elm[:newatt] = 'added string'
end

error:

can't write unknown attribute `newatt'

Answer 1

try this

class Test < ActiveRecord::Base
  attr_accessor :newattr
end

you can access it like

@test = Test.new
@test.newattr = "value"

As you may notice this a property, not a hash. so it uses . syntax. however, if you need it to behave like an hash you can do this without defining a new attribute

@test.all
@test.each do |elm|
    new_elm = {}
    new_elm[:newatt] = 'added string'
end

Lastly, I am not exactly sure what you are trying to do. if this doesn't make sense to you, kindly rephrase your question so we can understand the problem better.

Answer 2

I think you mean to assign @test to the ActiveRecord query, correct? Try:

@test = MyARClass.select("*, NULL as newatt")
@test.each {|t| t[:newatt] = some_value}

Another related solution is to make it a singleton class method, though you'd have to jump though more hoops to make it writeable and I intuitively feel like this probably incurs more overhead

@test = MyARClass.all
@test.each do t
  def t.newatt
    some_value
  end
end

Using the second method, of course you'd access it via @test.first.newatt, rather than @test.first[:newatt]. You could try redefining t.[] and t.[]=, but this is starting to get really messy.